Condensation between layers of insulation?

You have effectively put a vapor barrier in the middle. Moisture can't pass through the xps and with the batts on top it is a cooler surface than the room.

That sounds reasonable offhand, bee. Also there might be the possibility that any air flow has been stopped or nearly so, removing any way for moisture to seep out so it condenses first.

I wonder if, in that area, if only unfaced insulation or even none, wouldn't be better to do. Concrete, contrary to what a lot of people think, and its appearance, will in fact leak moisture in through it, so stopping that possibility alone can't really be done at any reasonable cost.

HTH,

Twayne`

Yes, the XPS is essentially a vapour barrier. What I don't understand is why presence of the batt would create a temperature differential large enough to cause condensation (more specificially, wouldn't temperature difference between air and exposed XPS be similar)?

My assumption here is that moisture is coming from the ambient air (which has relatively high humitidy...air exchanger is currently on the fritz). Once covered with a plastic vapour barrier, that ambient moisture will no longer be able to condense inside the wall. Valid thought? FWIW, I've been instructed to cut slits in the XPS to reduce the double vapour barrier effect.

first question before anyone can answer you is:

are you talking about a concrete BASEMENT wall or an OUTSIDE wall?

Mark

Basement, approx. 7' below grade.